Process for treating oil well formations



Unite .l

PROCESS FOR TREATING OIL WELL FORMATIONS No Drawing. Application July30, 1954, Serial No. 446,973

7 Claims. (Cl. 166-38) The present invention relates to a process fortreating oil wells by heating a subterranean oil-bearing formationpierced by a bore hole to remove from portions of the formation adjacentthe bore hole deposits or accumulations of substances which interferewith the production of petroleum from it. More particularly, thisinvention relates to a process for introducing into and about theformation an alkali metal which has been conditioned to spread over theexposed areas and to penetrate within the pore spaces and interstices ofthe formation so that the heat liberated upon reaction of the alkalimetal with States Patent O formation water, or water introduced into theformation,

will be effective both at the exposed surface in the bore hole and indepth into the formation to accomplish the desired removal of thedeleterious substances.

It is known in the art of producing petroleum from subterraneanformations that various substances may precipitate or otherwise separatefrom the petroleum as it flows from the formation to the well bore andgradually accumulate in the portions of the formation adjacent the wellbore and on the surface of the formation exposed in the Well bore. Suchaccumulations act to block off and continuously reduce the flow ofpetroleum into the well until, eventually, the production from the wellis so seriously affected it may be uneconomical to continue itsoperation. Deposits of waxes, parafiins, bitumens, asphalts, andmiscellaneous resins in well bores are familiar problems for theirunfavorable effects in this regard, and various processes and deviceshave been employed to remove them, some with more or less success. Forconvenience and simplicity, the types of deposits in which we areinterested, of which the foregoing are cited only by way of example,will hereafter be termed waxes, and the method of the invention will bedescribed in relation to such waxes.

It has been proposed heretofore to introduce sodium metal and water intoa well bore in a manner to cause the sodium to be reacted in the regionof an oil-bearing formation with the water so that the heat produced bythe reaction would melt the waxy deposits that were blocking theformation. Such proposals also contemplated a beneficial action from thehot sodium hydroxide produced by the reaction acting on the formationand also some benefit from a scrubbing action which would occur incidentto the evolution of hydrogen gas to agitate the hot reaction productsacross the exposed face of the formation to remove deposits therefrom.In the prior art, sodium metal was used in a mass of appreciable size,such as in pellet or brick form, and was placed in the bore holeapproximately at the position of the oil-bearing formation where it wasreacted with water. Necessarily under such conditions, the reactionwould take place in a localized portion of the bore hole, and the heatgenerated would, in effect, be concentrated primarily in the immediatevicinity of the sodium metal mass. The heat would be diffused from thislocus along the well bore 'and over the exposed face of the formation bythe agitation-of the water and reaction products generated by theliberation of gases resulting from the reaction, as well as by heatconduction through theelements of the formation.

.It is an object of this invention to provide a novel method fortreating a subterranean formation to free it of waxy deposits which havea deleterious effect on the production of oil from it.

Another object of the present invention is to treat a subterraneanformation with an alkali metal or an alloy of alkali metals which hasbeen conditioned before introducing it into the bore hole to place it ina form that will enable it to be spread over the exposed face of theformation and be forced into the interstices and pore spaces of theformation for an appreciable depth beyond the exposed face so that theexothermal effects of the reaction of the metal with water will bepronounced both in area and in volume.

It is a further object of this invention to treat a subterraneanformation to remove waxes from it by introducing into the formation awax solvent in which has been dispersed an agent which will reactexothermally with water in the formation to heat up the wax solventabove the formation temperature to enable it more effectively todissolve the waxes and assist the removal of them from the formation. 1

Other objects and advantages of this invention will become apparent asthe description of it proceeds hereinafter.

As one illustrative embodiment of a reactive agent useful in thisinvention, a dispersion of sodium metal is made in a carrier which isinert to it. Preferably, although not necessarily, the carrier is a waxsolvent and may be, for example, a crude oil, a highly aromaticpetroleum fraction, or a refined petroleum product. 802 extracts ofdiesel fuel and S02 extracts of kerosene have been found to beespecially effective as solvents of waxes found in oil wells and aresuitable for the purpose of this invention. The sodium dispersion may bemade by violently mixing the metal into the carrier by a mechanicalagitator until the sodium is reduced to particle sizes which will remaindispersed. Particles ranging in size from sub-micron to 5 microns aredesirable because this size range is advantageous for migrating into asubterranean formation. A particle size of less than 1 micron ispreferable for this purpose. Dispersing aids or stabilizers, such aslong-chain fatty acids, silicone oil or other suitable surface-activeagents, may be added and the carrier and metal may be heated to aid theformation of the dispersion. Dispersing aids may be selected which alsowill affect the rate of reaction of the sodium with water, to controlthe rate at which heat is liberated by the reaction.

Instead of sodium metal, an alloy of sodium and potassium metals may beused. The proportions of metals in the alloy may be selected so that thealloy is a liquid at ordinary temperatures and the dispersion will bethat of the liquid alloy in the liquid carrier. Under thesecircumstances, there is obviously no criticality of particle size of theliquid alloy for the best effect on the formation. Lithium, potassium,rubidium and cesium also may be used separately or in combination as thereactive agent.

In carrying out the steps of the present invention, the dispersion ofalkali metal in its inert wax-solvent carrier may be introduced into thebore hole by one of several means. Care must be taken to remove alltraces of water from the conduits through which the alkali metal dispersion is to be introduced, including the well tubing or casing down tothe location of the oil-bearing formation. If, for example, thedispersion is to be introduced into the well through tubing, a slug ofthe water-free carrier for the dispersion is introduced into the tubingprior to plac- Patented July 16, 1957.

ing the dispersion in it, and the slug of carrier is forced down to thelocation of the formation to clear all water from the path to be takenby the dispersion. A quantity of alkali metal dispersion is then placedin the tubing, followed by another slug of the carrier alone. If it isnecessary to do so, the final slug of carrier is placed under pressureto force the quantity of sodium dispersion down to the elevation of theformation. Sufiicient pressure is placed on the quantity of dispersionto cause it to migrate into the formation a predetermined distance.cases, the hydrostatic head of the products in the tube may besufiicient for this purpose.

As the alkali metal distributes itself over the exposed face of and intothe formation, it will contact the connate water therein and react withit to produce heat. The initial quantities of alkali metal will reactwith the water nearest the exposed face of the formation, causing thatportion of the formation to be heated first. Subsequent particles ofalkali metal migrating through the heated zone may become melted beforethey reach additional water with which to react. The melting of thealkali metal will aid it in progressing into the formation. Hence, theprocess of heating the formation in volume will continue until all ofthe alkali metal or water is used up. When it is desired to produce moreheat than the available water in the formation will permit, additionalwater may be added from the surface, as required.

Another way of introducing the dispersion into the well is by the use ofa proportioning pump. In this procedure, a liquid carrier iscontinuously pumped into the Well and predetermined proportions of aconcentrated dispersion automatically are added to it from anappropriate tank to give the desired proportion of alkali metal at thelocation of the formation.

It is also within the concept of this invention that the alkali metaldispersion or a liquid alloy of alkali metals may be introduced into thebore hole in a sealed container which can be transported down to theelevation of the subterranean formation to be treated and then rupturedto release the reactive material. In this latter case, care must betaken to make sure the bore hole is substantially free from water at thelocation of the formation so that the reactive material will not allreact in the bore hole before it can be forced into the formation.

Preferably, after the dispersion of sodium or other alkali metal oralkali metal alloy has been introduced into the formation, the well isshut-in for a time to insure reaction of the alkali metal with formationwaters and the proper distribution of heat throughout the formation. Forexample, the well may be shut-in from 1 to 4 hours to produce thedesired result. While the formation and the reaction products are stillwarm, the well is placed on production, and the Waxes dissolved in thecarrier, as well as the reaction products of the alkali metal with theformation water, will be produced out of the well to free the formationfor the subsequent production of petroleum.

As an illustrative example of some of the conditions which apply to thepractice of this invention, the relationships which follow from the useof a dispersion of sodium metal in a Wax solvent liquid hydrocarboncarrier, as de scribed hereinbefore, will be set forth. It will beapparent that such a dispersion will have many of the physicalcharacteristics of a liquid.

The volume of solution required per linear foot of treated formation forinjection to a distance rz feet from the center of a Well radius rw feetmay be obtained from the formula Gallons solution per foot of formation=0.24 (rz rz f In some 1 4 proach quantitative reaction with the connatewater in the formation will be given by the equation 13s., Sw

where Sw is the percent of pore space filled with water.

The theoretical temperature increase in degree F. from the reactionunder adiabatic conditions may be determined from the relationship F.temperature rise=0.066f (100-Sw) (lb. Na per gal. solvent) (HI) F.=0.85f Sw (IV) again assuming no heat loss to surrounding rock or fluids. Thefollowing calculations illustrate for a hypothetical case the valuesthat result from the above relationships: Let

Pounds sodium per gallon of solvent: (II) By substituting the numericalvalues in the equations set forth above, it can be determined fromEquation I that it will require 18 gallons of dispersion per foot offormation to fill it to a distance 2 feet from the center of the hole.

From Equation II above, it can be determined that there will be required3.25 pounds of sodium per gallon of carrier to achieve quantitativereaction with the connate water in the formation under the conditionsspecified.

From Equation III it can be determined that the theoretical temperaturerise of the treated portion of the formation when a dispersion of onepound of sodium metal per gallon of dispersion is used will be F.maximum.

From Equation IV, it can be determined that the temperature riseresulting from using enough sodium for quantitative reaction with thewater present will be 340 F. maximum.

The above temperature increases are theoretical and are not obtained inpractice since some heat transfer must exist in the formation. Also,there is the possibility that not all of the dispersed sodium willpenetrate into the formation or be reacted with water therein.Therefore, it is desirable to adopt a factor which will depend on theparticular formation and hole conditions to decrease the theoreticalcalculated amount to a value which will be encountered practically inthe field. This factor will be between 0.1 and 0.5, depending onspecific conditions indicated above. However, even the 0.1 factorindicates there will be an appreciable temperature rise in thesubterranean formation-following the practice of this invention.

It will be apparent that heating the formation in the manner set forthherein will have several beneficial effects in freeing it fromdeleterious waxy deposits. The heat of reaction of the alkali metal withthe formation Water will, in itself, cause melting of some such depositsand the subsequent freeing of the formation. Just as important as thiseffect, however, is that created by raising the temperature of the waxsolvent which is a carrier for the dispersed reactive metal. As thetemperature of the solvent is raised, it becomes increasingly moreeffective to dissolve the waxes from the formation and thereby free itfor production of oil. Since the dispersion, including both the waxsolvent and the reactive agent, has been caused to migrate into theformation in depth, there will take place more than a heating andcleaning of merely the exposed surface of the formation, but the effectof heat and solvent will reach beyond the exposed surface to remove thewaxes that have been deposited in the pore spaces and interstices atsome distance from the face.

It will be obvious that the method of this invention can be practiced byother specific apparatus and agents than those set forth above asexemplary embodiments without departing from the inventive concept, andit is intended to include all modifications and variations which fallwithin the scope of the appended claims.

I claim:

1. The method of treating an oil well which comprises introducing intosaid well a dispersion of alkali metals in a liquid wax solvent carrierwhich is inert to said metals, placing said dispersion under pressure toforce a portion of said alkali metals and said liquid wax solventcarrier into an oil-bearing formation to allow said alkali metal toreact with the water contained within said formation to raise thetemperature of said wax solvent, reacting the remaining portion of saidalkali metals with water in said oil well, and removing the reactionproducts and wax solvent carrier and dissolved waxes from said wellwhile the temperature of said products and carrier is above the normaltemperature of said well.

2. The process of treating an oil well which comprises introducing intosaid well a particulated alkali metal having particles ranging in sizefrom sub-micron to microns and contained in a wax solvent fluid carrierWhich is inert to it, placing said carrier and particulated alkali metalunder pressure in the well to force some of said particles and waxsolvent to migrate into an oil-bearing formation to allow said alkalimetal to react with the water contained therein and heat said formationand said wax solvent, and removing the products of reaction anddissolved waxes from said oil well.

3. The process for treating an oil-bearing formation penetrated by awell bore to free said formation of waxy deposits which comprisesintroducing into said well bore a dispersion of sodium in a liquid waxsolvent carrier for it, positioning said dispersion in said carrier atthe location of said oil-bearing formation and placing said dispersionand carrier under a pressure greater than the pressure existing in saidformation to force said dispersion and carrier into said formation toallow said sodium to react with the water contained within saidformation, and thereafter removing the products of reaction and the waxsolvent and dissolve the waxes from said formation.

4. The process for treating an oil-bearing formation in an oil well tofree it of waxy deposits comprising introducing a quantity of a liquidwhich is inert to sodium into the well bore, immediately thereafterintroducing a predetermined amount of a dispersion of sodium in saidliquid into said well bore, immediatelythereafter introducing a furtherquantity of said liquid into said well bore, transporting saidquantities of liquid and the included amount of said dispersion ofsodium to a position where said dispersion of sodium is at the locationof said formation, and at said location placing said dispersion ofsodium under a pressure greater than the pressure in said formation tocause particles of the dispersed sodium and a portion of said liquid toenter said formation to allow said sodium to react with the watercontained therein and subsequently removing said liquid and the reactionproducts of said sodium from the well bore.

5. The process for treating an oil well which comprises introducing intosaid well a dispersion of sodium metal in a liquid solvent for wax,placing said dispersion under pressure to force particles of the sodiummetal and portions of said solvent into an oil-bearing formation, toallow said sodium metal to react with water in said well and within saidformation, and thereafter removing the products of the reaction togetherwith the wax solvent and dissolved waxes from said oil well.

6. A method for treating an oil well which comprises introducing aliquid alloy consisting essentially of sodium metal and potassium metalinto said oil well, placing said liquid alloy under pressure to forcesaid alloy into an oilbearing formation, to allow said alloy to reactwith water within said formation, and removing the products of reactionfrom said oil well.

7. A method of treating an oil-bearing formation penetrated by a wellbore to free said formation of waxy deposits and water which comprisesremoving substantially all the water from the portion of said well boreadjacent the formation to be treated, introducing into saidsubstantially water-free portion of said well bore an aromatic waxsolvent inert to alkali metal and containing dispersed therein alkalimetalparticulated into sizes ranging from submicron to five micron,placing said wax solvent dispersion under pressure sufliciently greaterthan the pressure in said formation to force said solvent dispersionsubstantially into said formation to allow said alkali metal to reactwith the water in said formation and to raise substantially thetemperature of the wax solvent within said formation, whereby thesolvent power of the solvent wax is greatly increased, and removing thereaction products of alkali metal with water in the solvent anddissolved waxes from said formation and said well bore while thetemperature of said products, solvent and dissolved waxes is appreciablyabove the normal temperature of said formation.

References Cited in the file of this patent UNITED STATES PATENTS2,089,479 Herbsman Aug. 10, 1937 2,218,306 Austerman Oct. 15, 19402,672,201 Lorenz Mar. 16, 1954 OTHER REFERENCES Reistle: ParafiinBureauof Mines Bulletin 348, pages 83 to 84. Govt. Printing Office, 1932.

UNITED STATES PATENT OFFICE Certificate of Correction Patent No.2,799,342 July 16, 1 957 A 13:- W Irving Fatt "9 Is is hereby certifiedthat error appears in the printed specification of above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 68, after well and before radius insert of; same column,lines 71 and 72, the formula should read as shown below instead of as inthe patent- Gallons solution per foot of formation =0.24 (71 -73 f (I)Signed and sealed this 24th day of September 1957.

[SEAL] Attest: l

KARL H. AXLINE, ROBERT C. WATSON, Attestimg Ofiicer. 'ommissioner ofPatents.

1. THE METHOD OF TREATING ON OIL WELL WHICH COMPRISES INTRODUCING INTOSAID WELL A DISPERSION OF ALKALI METALS IN A LIQUID WAX SOLVENT CARRIERWHICH IS INERT TO SAID METALS, PLACING DISPERSION UNDER PRESSURE TOFORCE A PORTION OF SAID ALKALI METALS AND SAID LIQUID WAX SOLVENTCARRIER INTO AN OIL-BEARING FORMATION TO ALLOW SAID ALKALI METAL TOREACT WITH THE WATER CONTAINED WITHIN SAID FORMATION TO RAISE THETEMPERATURE OF SAID SOLVENT, REACTING THE REMAINING PORTION OF SAIDALKALI METALS WITH WATER IN SAID OIL WELL, AND REMOVING THE REACTIONPRODUCTS AND WAX SOLVENT CARRIER AND DISSOLVED WAXES FROM SAID WELLWHILE THE TEMPERATURE OF SAID PRODUCTS AND CARRIER IS ABOVE THE NORMALTEMPERATURE OF SAID WELL.